RDMA/mlx5: Remove duplicated assignment to resp.response_length

The assignment to resp.response_length is never read since it is being
updated again on the next statement. The assignment is redundant so
removed it.

Fixes: a645a89d ("RDMA/mlx5: Return ECE DC support")
Link: https://lore.kernel.org/r/20200604143902.56021-1-colin.king@canonical.com
Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/mlx5/qp.c

@@ -4162,8 +4162,6 @@ static int mlx5_ib_modify_dct(struct ib_qp *ibqp, struct ib_qp_attr *attr,
 
 		if (udata->outlen < min_resp_len)
 			return -EINVAL;
-		resp.response_length = min_resp_len;
-
 		/*
 		 * If we don't have enough space for the ECE options,
 		 * simply indicate it with resp.response_length.